This application for a Research Scientist Award is for the support of two lines of research. The first is an attempt to develop diverse psychometrically sound cognitive markers of the predisposition to schizophrenia. The research plan focuses on psychometric problems that appear to be a major obstacle in this area. The tasks are ones that appear especially promising for measuring important but separate aspects of schizophrenic cognitive defect and that seem suitable for measuring the mild degree of cognitive defect that is expected in the nonpsychotic relatives of patients. The measures are: 1) associatively based semantic priming, which reflects persistence of associative arousal; 2) a version of the span-of-apprehension task, which measures attentional breadth; 3) defective comprehension in binaural listening, which is thought to reflect defective interhemispheric transfer; 4) the Navon task, which measures the failure to inhibit responses to stimuli that should be screened out to facilitate cognitive processing; and 5) a version of the Place and Gilmore task, which measures an aberrant perceptual response to groupings of stimuli. The psychometric problems of special concern are: 1) the artifactual curvilinear relationship in measures of differential deficit, for Tasks A and B, between the (A - B) difference score and the (A + B) score of overall accuracy, and 2) the effects of differential discriminating power of the two tasks coupled with differences among subjects in overall accuracy in yielding artifactual difference scores. The design solutions will be either the use of psychometrically matched tasks on the use of titration in which (A + B) overall accuracy is maintained at a constant level by manipulation of an appropriate stimulus variable. Schizophrenic, schizophreniform, and bipolar patients will be tested as well as relatives of patients and control subjects. The second line of research is a ten-year follow-up of 343 college students identified as psychosis prone by their scores on scales of psychosis proneness, and 158 control subjects. Laboratory findings, as well as the results of a two-year follow-up, indicate that this group is at elevated risk for psychosis.